Plasmablastic lymphoma: One or more entities?

Diffuse large B-cell lymphoma (DLBCL) is the most common type of B-cell lymphoma [1].Morphologic variants of DLBCL mainly include centroblastic, immunoblastic, anaplastic, and T-cell/histiocyte rich lymphomas [1].Plasmablastic lymphoma (PBL) is a rare variant of DLBCL originally described in the oral cavity in the setting of HIV infection [1,2].PBL has subsequently been reported in other sites [1,2].In this issue of the American Journal of Hematology, Castillo et al. [3] present the first extensive literature review of the epidemiology, clinical findings, pathology, treatment, and outcome of 112 patients with HIV-associated PBL.The authors point out that HIV-associated PBL tends to affect young men with CD41 counts less than 200 cells/mm 3 .The consistent presence of plasma cell markers and frequent absence of B-cell markers are key pathologic features of this entity [3].Tumors with plasmablastic differentiation typically occur in patients with an abnormal immune state (HIV positive, posttransplantation, or the elderly).These tumors often arise in the oral cavity or other mucosal sites of the head and neck [1,2], in the body cavity (primary effusion lymphoma -PEL) [4], or in association with multicentric Castleman disease (MCD) [5].In addition, a solid lymphoma/ extracavitary PEL/human herpesvirus 8 (HHV8)-associated DLBCL has been described, predominantly in HIV-positive patients that shows coexpression of Epstein Barr virus (EBV) (Table I) [6,7].All these lymphomas are composed of large cells with abundant cytoplasm and immunoblastic, anaplastic, or plasmacytoid morphology.Irrespective of morphologic type, tumor cells usually express a plasma cell-related phenotypic profile (CD381, MUM11, EMA1/2 CD301/2, CD451/2 (weak), conventional B, and T-cell markers).Morphologically, the PBL of the oral cavity is composed of a very monomorphic, sheet-like proliferation of immunoblasts.The other plasmablastic tumors tend to have a predominance of immunoblasts but show some cells with plasmacytic differentiation.The body cavity and extracavitary PELs have significant nuclear pleomorphism with plasmacytoid morphology in some cells.PBL with plasmacytic differentiation and DLBCL with secretory differentiation (immunoblasts and plasmacytoid cells) are distinguished by the presence of centroblasts in the latter.